1. Field of the Invention
This invention is in the field of nondestructive testing of objects by means of the penetrant inspection technique, and utilizes hydrophobic developing particles to render indications contrastingly visible to the background.
2. Description of the Prior Art
The present invention is concerned with the well-known "post-emulsification" technique of removing excess penetrant from a test piece being tested by the penetrant inspection method. The post emulsification technique is described completely in the DeForest et al. U.S. Pat. No. 2,806,959. As noted in that patent, the method involves employing an oily liquid penetrant having excellent penetrating properties but being immiscible with water and being substantially free of any emulsifying agent. The oily penetrant is then treated with an emulsifying agent which, by substantially static contact with the penetrant, renders the latter superficially water-emulsifiable. In a subsequent washing step with water, it is only the superficial emulsified layer of the penetrant that is removed with the excess of emulsifying agent. Any emulsified penetrant that has penetrated the surface discontinuities remains in such discontinuities and serves to indicate the existence and location thereof by the contrasting color effect that is obtained upon application of a developer to the surface. Where the penetrant is colored with a fluorescent dye dissolved in the penetrant, the inspection is carried out under "black" or ultraviolet light.
This type of process has been widely used commercially and is quite successful because it is capable of determining the presence of relatively shallow and relatively wide cracks, as well as the presence of defects having very fine surface openings. This is so because the non-water miscible penetrant is not washed out of such wide, shallow cracks and is better able to enter into the finer surface defects.
A specific improvement on the DeForest et al. patent is found in the Parker U.S. Pat. No. 2,978,418 which describes an improved emulsifier for the post emulsification process, the emulsifier containing from 1 to 20 percent by volume of tri-butoxyethyl phosphate.
Another type of improved emulsifier for the post emulsification process is described in Borucki U.S. Pat. No. 3,401,556. That patent deals with an emulsifier composition which is free from sulfur, chlorine and phosphorus and includes effective proportions of
1. a water miscible alkanol amine, PA1 2. tallol, PA1 3. a water miscible polymerized monohydroxy oxy 1,2-propylene aliphatic monoether which functions as a coupling agent, PA1 4. a non-ionic lauroyl diethanol amine wetting agent, PA1 5. an alkyl aryl polyether alcohol which imparts enhanced water washability to the resulting emulsifier, PA1 6. an isoparafinic hydrocarbon as a solvent, and PA1 7. water.
Still another emulsifier suitable for use in a post emulsification process is disclosed in Magdalin U.S. Pat. No. 3,585,853. This emulsifier is an aerosol foam-forming composition which includes water, a surfactant, a foaming agent, a coupling agent, and optionally a corrosion inhibitor.
The dry developers currently being used in the post emulsification-type process may consist of mixtures of silica aerogels, hydrated alumina aerogels and talc. These materials, however, are all hydrophilic which requires that the part, after emulsification with the emulsifier, be thoroughly washed with water and dried completely before the dry developer is applied. Otherwise, the finely divided hydrophilic particles pick up water and form a thin cake on the surface of the part which tends to obscure indications caused by penetrant exuding out of the cracks and into the powder.